First Place Winner, High School - 2009 Imagine That! Engineering Innovation

Address

Texas

New Energy and Luminance by Organic Solar Cells and OLEDs

“Let’s try 3.5 volts.”

The physicist sitting across from me gasped. A faint electro-luminance begins to flicker as the organic light emitting diode’s (OLED) electrons are recombining into holes and releasing their photons: a brilliant, natural glow. Organic.

It was a rather ingenuous device. After testing the prototypes in the labs, I would soon bring a proposal to build a structure in the city that I would name the Hourglass. The OLED bearing grey panels around surrounding the Hourglass lifted and folded within themselves, allowing sunlight to enter in day. At night, they would envelop the Hourglass for protection. The entire machine was meant to generate energy for the nearby city: the rings that encircled its center were sheets of organic solar cells, or organic photovoltaics (OPVs). They would harvest the energy and convert them into electricity by the disassociation of an exciton.

“How can you expect the devices to not crack and break during construction and use?” The physicist inquired.

After all, typical organic photovoltaics had an Indium Tin Oxide (ITO) anode layer, which made the device brittle and prone to damage from bending.

“Carbon nanotubes.” I mused, “Multi-walled carbon nanotubes.”

Instead of the brittle ITO, the organic solar cells incorporated the MWNTs into the solar cells, which were flexible and durable.

“At the molecular level, carbon nanotubes are stronger than both steel and diamond. They are lattices of carbon nestled within each other, created from carbon gas and an iron catalyst. They are grown into ‘forests’ and spun out onto wire jacks. Of course, it would require meticulous detailing and careful technical skills.”

The physicist was amused. So far, I had suggested a matrix of twelve Hourglasses throughout the city, providing the homes and corporations with the energy they needed from the sun. I had not mentioned that organic solar cells had finally reached efficiencies higher than that of their silicon-based inorganic counterparts, or even the thin-film photovoltaics.

“85% efficiency?” he cried in disbelief as I nodded and continued to draw the blueprint.

“Organic solar cells have never gotten to such high levels before. What makes you think that you can create an OPV with such incredible efficiency?”

I smiled and began to explain. The process was simple, really. Again, the carbon nanotubes were involved in the plan. However, this time, since the carbon nanotubes have a 3D matrix that extend into the organic layers, they allow for more percolation paths throughout the device. In other words, the solar cells would be more efficient once there are more paths for the carriers to penetrate the device. The current would increase, and the photon harvesting would consequently increase as well.

“What happens,” he asked, “if there is too much current running through the device. You have organic polymers: PBCM is one of them. Would they not burn with such high currents?”

My reply? “D-Sorbitol. Yes, that’s the artificial sweetener found in your gum. However, it also crystallizes easy and forms a shield around the organic molecules that prevents them from burning. While we might sacrifice some efficiency, hopefully the effectiveness of the carbon nanotubes mixed with the PEDOT:PSS hole blocking layer would balance it out. In the end, we will have an extremely efficient, extremely durable device. What else could you ask for the power source of a city?”

He chuckled. “Perhaps that will work. However, what do you propose to do with the inner grey panels. What are these…organic light emitting diodes, or OLEDs, that you always talk about?”

I pointed towards the bright panels lining the sides of the protection wall.

“These are cost effective forms of light that can be used for both aesthetic purposes and for guidance for engineers who need to repair the Hourglasses at nighttime. They can be turned on and off with the simple manipulation of voltage.”

“How exactly are they created?” he inquired, pulling the blueprint closer to him.

“Well,” I began, “They are, in essence, very similar to the organic solar cells. They are the reverse: while organic solar cells absorb light and create electricity, OLEDs use electricity to generate light. They have the same structure, and their only difference lies in their organic layers: while solar cells have PBCM, OLEDs may have a range of polymers and molecules, from PFO to alpha-NPD and Alq3.”

Pointing to the blueprint of my plan, I continued, “They can be created on plastic substrates, which gives them the ability to be bent and molded to the curved shape of the walls. Don’t you see? They add aesthetic pleasure for tourists of the Hourglass, but they’re also practical for repairmen.”

Engineers have to consider all aspects of a design: the science, the aesthetics, the practicality. Before the blueprint would go into effect, I would also have to write proposals and convince the city council to make a budget for the Hourglass. Taking the cost into consideration, I had opted for more cost effective materials: plastic substrates, carbon nanotubes (carbon being abundant in the biosphere), simple yet sturdy organic polymers, and an aluminum cathode. While gold cathodes have a higher difference in work function from the anode and would result in a brighter device, I decided that the OLEDs only required 2000 candela to light the pathways of the Hourglass.

The physicist smiled. “Tell me, Miss Yang, do you see any problems with your plan? It seems rather farfetched.”

As a woman engineer, I must have the conviction to follow through with the plan. While I have the passion for science, unless I strongly believe in the success of this combined solar cell – OLED matrix, the city council might not be convinced. I looked towards the glowing OLED 4 feet away, a miniature prototype of the larger scale OLEDs in my plan.

“No, I don’t see any impossible problems.” While there may be some, as an engineer, it is my job to find a way to make it happen.

The 2018 EngineerGirl Writing Contest

Also, don't forget to look for our EngineerGirl booth at Invent It. Build It.(IIBI) IIBI is a hands-on engineering experience for girls in grades 6-12, and their families. Join 10,000 women engineers from around the globe in Austin, TX on Saturday, October 28th to prove that girls can be engineers!